28 REPORT — 1875. 



Expenmenis on Magnetized Rings, Plates, and Disks of Hardened Steel, 



By P. Bkaham. 



On the Decomposition of an Electrolyte hy Magneto-Electric Induction *. 

 By J. A. Fleming, B.Sc. {Lond.), F.C.S. 



When a solid conductor is moved on a magnetic field induced cun-ents are 

 created in it. In a solid these expend themselves partly or wholly in producing 

 heat in the conductor. This paper is occupied with an examination of the effect 

 produced on electrolytes under the same circumstances, viz. when made to flow or 

 move in a magnetic field. Experiments are described to show, first, that induced 

 currents are produced under these conditions in electrolytes, and then that the 

 electroljiie is to some slight extent decomposed by these currents. 



The experiment which gives gi-oxmds for making this statement may briefly be 

 described thus : — A glass tuhe, 2 centims. in diameter, has platinum plates placed 

 in its interior at the sides ; these are welded to platinum wires sealed through the 

 ^lass. The tuhe is supported between the poles of a powerful electromagnet 

 in such a way that the tube is perpendicular, and the line joining the plates is at 

 right angles to the line joining tlie poles. This tube is connected, by means of a 

 siphon, with a reservoir of dilute sulphm-ic acid, placed at a height of ahout 

 3 metres above the floor. After filling the tube and siphon and carefully depo- 

 larizing the plates, the magnet is magnetized by a current from twenty Grove's 

 cells, and then the plates connected by wires with a delicate mirror-galvanometer 

 in another room. 



On allowing the liquid to flow down, the galvanometer indicates a cun-ent 

 passing across fi:om one platinum plate to another; this is the induced cuiTent 

 created by the flow of the liquid in the magnetic field. Various and numerous 

 precautions have to be taken to prevent any movement or vibration of the platinum 

 plates and variation in the strength of the field. The magnet being kept mag- 

 netized, the plates are then short-circuited, after having been carefully depolarized, 

 and the liquid allowed to flow down. When the acid is nearly exhausted, this 

 shorty circuit is broken and the flow of the liquid immediately after stopped. 

 On joining the plates to the galvanometer a reverse current is now perceived — that is, 

 one opposite in dii-ection to the real induced current. This indicates that the 

 plates have become polarized again hy the effect of the induced current created 

 by the flow of the electrolyte in the magnetic field. It was found that this polari- 

 zation could be rendered more decided by covering over the platinum plates with a 

 layer of coarse cloth, or by placing a cloth tuhe in the interior of the glass one in 

 such a way that the liqiud flows down the imide of this tube, but the platinum 

 plates are on the outside. The reason of this is because the rapid downrush of the 

 liquid mechanically clears away the film of gases from the plates, and so renders 

 the polarization less than it should be. 



In the last part of the paper the question is raised of how far the foregoing facts 

 may have interfered with the success of Faraday's experiment on the flow of the 

 Thapes at Waterloo Bridge. Since this polarization introduces a reverse electro- 

 motive force, unless the electromotive force due to the strength of field and velo- 

 city and width of stream is greater than that required to decompose water, no 

 permanent current can be produced in an electrolyte flowing in a magnetic field 

 but only a transient one, the strength of the induced ciu-rent rapidly decreasing as 

 it polarizes the electrodes. 



On the Position of the Magnetic Equator in the Gulf of Biam and in the Gulf 

 of Bengal. By Dr. J. Janssen. 



Dr. Janssen made observations at Bangkok, Bangchallo, Ligor, Singora, and Sin- 

 gapore ; and he concludes that the magnetic equator passes between Lio-or and 

 Smgora about 7° 43' north latitude. " 



* Published in extenso in the 'Electrical Kews,' September 2, 1875. 



